Synchronize CopulaGAN and CTGAN hyperparameters

[csala]

PRs #334 and #277 introduced new CTGAN hyperparameters that are not properly exposed in the CopulaGAN class, either because they are just not there, like pac, or because they are not listed in the docstring, like discriminator_lr.

CopulaGAN should be updated to ensure that all the available CTGAN hyperparameters are both exposed and described in the docstring.